Comparative Study of Design Forces of Cast-In-Place Reinforced Concrete Diaphragms in Different Standards

Diaphragms are horizontal elements of the lateral force-resisting systems in structures. In addition to resisting the gravity loads, reinforced concrete diaphragms play a vital role in transmitting seismic loads to vertical force-resisting elements such as columns, shear walls or braces. It is necessary to design the diaphragms in such a way to avoid any disturbances in the load path. Various approaches with different procedures are provided in standards and codes for calculating diaphragm design forces. One of these differences is the effect of the type of diaphragm on determining the design force. For example, in the alternative method provided in the American loading code force reduction coefficients according to the diaphragm type are suggested, while in the general method of the same code and in the method provided in the New Zealand seismic loading standard for all diaphragms consider only one force calculation method. In this article, the methods for calculating the design force of cast-in-place reinforced concrete diaphragms in the loading standard of the United States and New Zealand as the advanced standards in seismic design of structures are introduced and compared.